This invention relates to a method for making a negative type lithographic printing plate using a novel method for forming images by negative type silver complex diffusion transfer processes.
It is well known that a silver image is produced by silver complex diffusion transfer processes and is used as a lithographic printing plate by subjecting the silver images to oleophilization treatment.
That is, according to the above method, a silver halide emulsion layer coated on a support is imagewise exposed and then treated with a processing solution containing a developer and a silver halide solvent to reduce exposed silver halide to non-clustered silver and to dissolve unexposed silver halide by the action of the silver halide solvent, which is precpiitated as a physical developed clustered silver on physical development nuclei provided in contact with the emulsion layer and thus obtained positive silver image is made oleophilic whereby this can be directly used as a lithographic printing plate. This technique is disclosed, e.g., in Japanese Patent Publication (Kokoku) Nos. 10910/61, 18719/61, 30562/73, etc.
However, the printing plates made by methods of plate making using the above diffusion transfer process are positive type printing plates and so these methods cannot be used for making lithographic printing plates directly from negative originals.
Furthermore, theoretically, negative type is more useful than positive type for direct plate making by laser scanners which are recently widely employed.
On the other hand, there have been known only a few methods for making lithographic printing plates with use of a negative type silver complex diffusion transfer process. One of them recently proposed is disclosed in Japanese Patent Laid-Open Application (Kokai) No. 44153/82 according to which non-light-sensitive easily-soluble metal salt particles coated with an insolubilizing agent are dissolved out by the physicochemical action caused by development of light-sensitive silver halide in the exposed areas to form a metallic image, which is made oleophilic. Improvement of this method is disclosed in Japanese Patent Laid-Open Application (Kokai) No. 150849/82. However, in these methods a metal salt particle coated with an insolubilizing agent is used as a negative image forming material and therefore the image forming speed on developing is low and moreover since the light-sensitive material contains an insolubilizing agent for the metal salts in a large amount, the storage property of the material is badly influenced.